Organic aluminoxanes are one form of aluminoxy compound. Organic aluminoxanes can be produced by the partial hydrolysis of hydrocarbyl aluminum compounds. Such aluminoxanes have been found useful in a variety of chemical reactions, including utility as catalyst components for polymerization catalysts, especially in high activity metallocene catalyst systems.
The combination of such aluminoxanes with metallocenes has been shown to be useful for certain types of olefin polymerization. One of the earliest patents containing such a disclosure is U.S. Pat. No. 3,242,099, the disclosure of which is incorporated herein by reference. Such metallocene catalysts have been used in homogeneous solution polymerization. Since such homogeneous catalyst systems are soluble in the polymerization medium it is generally observed that the resulting polymer has low bulk density.
Further, attempts to use metallocene/aluminoxane catalysts in a slurry or particle form type polymerization have not heretofore been found to be commercially feasible. In slurry or particle form polymerization, the polymerization conditions are selected such that the polymer forms as discrete particles which are insoluble in the polymerization reaction medium during the polymerization. It has been observed that when such particle form polymerizations are carried out in the presence of a metallocene/aluminoxane catalyst system, large amounts of polymeric material are formed on the surfaces of the polymerization vessel. This fouling is particularly detrimental in a particle form process since it produces an adverse effect on the heat transfer and also results in the need for periodic if not continuous cleaning of the reactor. In order to have a metallocene/aluminoxane catalyst useful in a commercial continuous particle form process such as those using a loop reactor, it is necessary to have a catalyst system which will not cause significant amounts of reactor fouling.
It is known that a solid form of aluminoxane can be obtained by treating a commercial organo aluminoxane solution with a countersolvent; however, even that solid has been found to cause reactor fouling in slurry polymerizations. Even when a countersolvent is used to precipitate the aluminoxane onto an insoluble particulate carrier reactor fouling is still a problem in slurry, i.e. particle form polymerization.
An object of the present invention is to provide a new organo-aluminoxy composition which while still active as a cocatalyst for a transition metal polymerization catalyst, at the same time does not produce significant reactor fouling in a particle form process.
Another aspect of the present invention relates to a method for making this new organo-aluminoxy composition.
Still another aspect of the present invention relates to polymerization catalyst systems comprising a transition metal compound and the new organo-aluminoxy composition.
Still yet another aspect is to provide a solid organo-aluminoxy composition having a surface area greater than that of the solid resulting from the vacuum stripping of an aluminoxane solution. Inventive solids having a surface area as high as 300 m.sup.2 /g as determined by a BET test have been prepared.
Another object is to provide a stable solid metallocene polymerization catalyst comprising the combination of a metallocene and the inventive solid aluminoxane.
Still yet another aspect of the present invention relates to the polymerization of olefins using the new organo-aluminoxy composition as the cocatalyst, especially in particle form polymerizations.
Other aspects, objects and advantages of the present invention will become apparent to those skilled in the art having the benefit of the following disclosure.